Method of continuous recovery of (meth)acrylic acid and apparatus for the method

ABSTRACT

The present invention relates to a continuous recovery method of (meth)acrylic acid and an apparatus for use in the recovery method. A continuous recovery method of (meth)acrylic acid according to the present invention can ensure a high recovery rate of (meth)acrylic acid through a solvent recovering process in addition to enabling the stable recovery of (meth)acrylic acid and the operation of continuous processes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.16/078,956, filed on Aug. 22, 2018, and published as US 2019/0054395 onFeb. 21, 2019, which is the U.S. national stage entry of InternationalApplication No. PCT/KR2017/012619, filed on Nov. 8, 2017, which claimsthe benefit of Korean Patent Application No. 10-2016-0158615 filed onNov. 25, 2016, with the Korean Intellectual Property Office, all ofwhich incorporated by reference in their entirety as if fully set forthherein.

TECHNICAL FIELD

The present invention relates to a method of continuous recovery of(meth)acrylic acid and an apparatus for the method.

BACKGROUND OF ART

(Meth)acrylic acid is generally prepared by gas phase oxidation ofpropane, propylene, (meth)acrolein, and the like in the presence of acatalyst. For example, propane, propylene, and the like are converted to(meth)acrylic acid through (meth)acrolein by gas phase oxidation in thepresence of an appropriate catalyst in a reactor, and a reaction productmixed gas including (meth)acrylic acid, non-reacted propane orpropylene, (meth)acrolein, an inert gas, carbon dioxide, water vapor,and various organic by-products (acetic acid, heavies, and the like) isobtained in the back end of the reactor.

The (meth)acrylic acid-containing mixed gas contacts with an absorptionsolvent including water in a (meth)acrylic acid absorption tower, and isrecovered as a (meth)acrylic acid aqueous solution. Further, a(meth)acrylic acid-stripped insoluble gas is recycled for a synthesisreaction of (meth)acrylic acid, and a part thereof is incinerated,converted into harmless gas, and discharged. The (meth)acrylic acidaqueous solution is extracted, distilled, and purified to obtain(meth)acrylic acid.

Meanwhile, various methods of controlling process conditions or aprocess sequence and the like to improve the recovery efficiency of(meth)acrylic acid have been suggested. Among them, a method is knownwherein a part of the (meth)acrylic acid aqueous solution obtained in a(meth)acrylic acid absorption tower is fed to an extraction tower, a(meth)acrylic acid extract with reduced water content and the raffinateare obtained using a hydrophobic solvent, and the extract and theresidue that is not fed to the extraction tower, among the (meth)acrylicacid aqueous solution obtained in the absorption tower, are distilledtogether.

Further, a method for reducing energy consumption is known, byselectively discharging an aqueous solution including (meth)acrylic acidof a low concentration at the middle stage of the absorption tower toobtain a high concentration (meth)acrylic acid aqueous solution at thelower part of the absorption tower, feeding the low concentration(meth)acrylic acid aqueous solution discharged at the middle stage ofthe absorption tower to the extraction tower, obtaining a (meth)acrylicacid extract with reduced water content and the raffinate using ahydrophobic solvent, and feeding the high concentration (meth)acrylicacid aqueous solution and the (meth)acrylic acid extract to thedistillation tower and conducting azeotropic distillation.

However, according to the known method of continuous recovery of(meth)acrylic acid, if the amount of the hydrophobic solvent in theextraction tower is increased so as to increase the (meth)acrylic acidextraction rate, the amount of the azeotropic solvent subsequently fedto the feed stage of the water separation tower may increase, the amountof the solvent fed to the water separation tower should be constantlymaintained for the azeotropic distillation of water and solvent so thatthe content of (meth)acrylic acid in the upper discharge liquid of thewater separation tower may be low, and thus the amount of the solventintroduced into the water separation tower as reflux may decrease, and achange in gas/liquid behavior in the water separation tower may begenerated. Thus, as the upper tray of the water separation tower isdried, the separation efficiency of the water separation tower maydecrease, and (meth)acrylic acid recovery rate may decrease.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

It is an object of the present invention to provide a method forcontinuous recovery of (meth)acrylic acid that can secure a high(meth)acrylic acid recovery rate, and simultaneously, can secure moreimproved operation stability.

It is another object of the present invention to provide an apparatusthat can be used for the continuous recovery of (meth)acrylic acid.

Technical Solution

The present invention provides a method for continuous recovery of(meth)acrylic acid, including the steps of:

contacting a mixed gas including (meth)acrylic acid, organicby-products, and water vapor, produced by the synthesis reaction of(meth)acrylic acid, with water in a (meth)acrylic acid absorption towerto obtain an aqueous solution of a low concentration (meth)acrylic aciddischarged at any one point corresponding to 30 to 70% from the highestpart of the absorption tower, and an aqueous solution of a highconcentration (meth)acrylic acid discharged to the lowest part of theabsorption tower;

contacting the low concentration (meth)acrylic acid aqueous solutionwith an extraction solvent including a hydrophobic organic solvent in a(meth)acrylic acid extraction tower to extract (meth)acrylic acid;

heating the obtained (meth)acrylic acid extract in a solvent recoverytower to recover the solvent; and

distilling the feed excluding the solvent recovered from the(meth)acrylic acid extract and the high concentration (meth)acrylic acidaqueous solution in a water separation tower to obtain (meth)acrylicacid,

wherein a weight ratio of the extraction solvent to water in the lowconcentration (meth)acrylic acid aqueous solution fed to the step ofextracting (meth)acrylic acid is 2.7 or more.

The present invention also provides an apparatus for continuous recoveryof (meth)acrylic acid, including:

a (meth)acrylic acid absorption tower (100) equipped with a mixed gasinlet to which a mixed gas including (meth)acrylic acid, organicby-products, and water vapor, produced by the synthesis reaction of(meth)acrylic acid, is fed, in which a low concentration (meth)acrylicacid aqueous solution outlet, at which a low concentration (meth)acrylicacid aqueous solution obtained by the contact of the mixed gas withwater is discharged, is installed at any one point corresponding to 30to 70% from the highest part, and a high concentration (meth)acrylicacid aqueous solution outlet is installed at the lowest stage;

a (meth)acrylic acid extraction tower (200) equipped with an aqueoussolution inlet that is connected with the low concentration(meth)acrylic acid aqueous solution outlet of the absorption tower (100)through an aqueous solution transfer line (103), an extract outlet atwhich a (meth)acrylic acid extract obtained by the contact of theintroduced (meth)acrylic acid aqueous solution with an extractionsolvent is discharged, and a raffinate outlet at which a raffinate isdischarged;

a solvent separation tower (250) equipped with an extract inlet that isconnected with the extract outlet of the extraction tower (200) throughan extract transfer line (203), an upper stage outlet at which thesolvent obtained by heating the introduced extract is discharged, and alower stage outlet at which the feed excluding the solvent recoveredfrom the extract is discharged; and

a water separation tower (300) equipped with a feed inlet that isconnected with the lower stage outlet of the solvent separation tower(250) through a transfer line (253), and is connected with the(meth)acrylic acid aqueous solution outlet of the (meth)acrylic acidabsorption tower (100) through a transfer line (102), and a(meth)acrylic acid outlet at which (meth)acrylic acid obtained by thedistillation of the introduced feed is discharged,

wherein the apparatus is operated such that a weight ratio of theextraction solvent to water in the low concentration (meth)acrylic acidaqueous solution fed to the (meth)acrylic acid extraction tower (200) is2.7 or more.

Hereinafter, a method of continuous recovery of (meth)acrylic acid and arecovery apparatus according to the embodiments of the invention will beexplained.

Unless otherwise described, terms used herein are defined as follows.

The term ‘(meth)acrylic acid’ generally refers to acrylic acid,methacrylic acid, or a mixture thereof.

Further, the term ‘(meth)acrylic acid-containing mixed gas’ generallyrefers to a mixed gas that may be produced when (meth)acrylic acid isprepared by gas phase oxidation. According to one embodiment of thepresent invention, the (meth)acrylic acid-containing mixed gas may beobtained by gas phase oxidation of at least one compound selected fromthe group consisting of propane, propylene, butane, i-butylene,t-butylene, and (meth)acrolein (‘raw material compound’) in the presenceof a catalyst, wherein the (meth)acrylic acid-containing mixed gas mayinclude (meth)acrylic acid, non-reacted raw material compounds,(meth)acrolein, an inert gas, carbon monoxide, carbon dioxide, watervapor, and various organic by-products (acetic acid, heavies, and thelike), and the like. Herein, ‘light ends’ or ‘heavies’ are kinds ofby-products that can be produced in the process of preparing andrecovering (meth)acrylic acid, and generally refer to compounds havingmolecular weights that are smaller than or higher than that of(meth)acrylic acid.

The term ‘feed’ refers to a liquid mixture containing solute to beextracted, and it may be a mixture of a solute that is soluble in anextraction solvent and an inert material that is not soluble in anextraction solvent. Herein, if the extraction solvent is added to thefeed, the solute is dissolved in the extraction solvent from the feed bymass transfer. Thereby, the extraction solvent in which a significantamount of solute is dissolved forms an extract, and the feed that isdeprived of a significant amount of solute forms a raffinate.

The term ‘(meth)acrylic acid aqueous solution’ refers to an aqueoussolution containing (meth)acrylic acid, and for example, it may beobtained by contacting the (meth)acrylic acid-containing mixed gas withwater.

In addition, the technical terms used herein are only to mentionspecific embodiments, and are not intended to limit the invention.Further, singular forms used herein include plural forms, unless theyhave clearly opposite meanings, and the meaning of ‘comprising’ as usedherein embodies a specific property, area, integer, step, operation,element, or component, and it does not exclude the addition of otherspecific properties, areas, integers, steps, operations, elements, orcomponents.

Hereinafter, referring to the attached drawings, specific embodiments ofthe invention will be explained in detail so that one of ordinaryknowledge in the art may easily practice it. However, the presentinvention may be embodied in various forms, and is not limited to theexamples.

I. A Method of Continuous Recovery of (Meth)Acrylic Acid

According to one embodiment of the invention, a method of continuousrecovery of (meth)acrylic acid is provided, including:

contacting a mixed gas including (meth)acrylic acid, organicby-products, and water vapor, produced by the synthesis reaction of(meth)acrylic acid, with water in a (meth)acrylic acid absorption towerto obtain an aqueous solution of a low concentration (meth)acrylic aciddischarged at any one point corresponding to 30 to 70% from the highestpart of the absorption tower, and an aqueous solution of a highconcentration (meth)acrylic acid discharged to the lowest part of theabsorption tower;

contacting the low concentration (meth)acrylic acid aqueous solutionwith an extraction solvent including a hydrophobic organic solvent in a(meth)acrylic acid extraction tower to extract (meth)acrylic acid;

heating the obtained (meth)acrylic acid extract in a solvent recoverytower to recover the solvent; and

distilling the feed excluding the solvent recovered from the(meth)acrylic acid extract and the high concentration (meth)acrylic acidaqueous solution in a water separation tower to obtain (meth)acrylicacid,

wherein a weight ratio of the extraction solvent to water in the lowconcentration (meth)acrylic acid aqueous solution fed to the step ofextracting (meth)acrylic acid is 2.7 or more.

The present inventors confirmed during studies on the continuousrecovery method of (meth)acrylic acid that, in the previously disclosed(meth)acrylic acid recovery method wherein a (meth)acrylic acid aqueoussolution is fed to an extract tower, a (meth)acrylic acid extract isobtained using a hydrophobic solvent, and the extract is distilled torecover (meth)acrylic acid, and if the amount of the hydrophobic solventis increased so as to increase the extraction rate, the amount of thesolvent introduced into the reflux of a water separation tower isdecreased, thus lowering the liquid/gas ratio in a tray existing in theupper region of the stage into which the extract is introduced.

Thus, it was confirmed that, since the liquid level, flood percentage,froth height, and the like in the tray existing in the upper region ofthe stage into which the feed of the water separation tower and theextract are introduced are significantly lowered compared to theprevious operation of the water separation tower using an optimum refluxsolvent, and the liquid/gas flow behavior in the upper tray of the waterseparation tower becomes unstable, various problems are generated suchas a decrease in the (meth)acrylic acid recovery rate in the waterseparation tower, and the like.

Therefore, as the results of continuous studies of the presentinventors, it was confirmed that if a solvent recovery process isintroduced between the (meth)acrylic acid extraction process anddistillation process as shown in FIGS. 1 and 2, solvents having a verylow concentration of (meth)acrylic acid may be recovered from thesolvent recovery tower, and it may be refluxed to the top of the waterseparation tower to increase the reflux ratio of the water separationtower, or it may be introduced into the phase separation tank existingin the upper part of the water separation tower and reused in theextraction tower and water separation tower, thus enabling the operationof a more economical and stable continuous process.

Hereinafter, referring to FIG. 1 and FIG. 2, each process that can beincluded in the embodiments of the invention will be explained.

Absorption Process

First, the continuous recovery method of (meth)acrylic acid according toone embodiment includes the step of contacting a mixed gas including(meth)acrylic acid, organic by-products, and water vapor, produced bythe synthesis reaction of (meth)acrylic acid, with water in a(meth)acrylic acid absorption tower to obtain the aqueous solution of(meth)acrylic acid, and an absorption process throughout thespecification means a process for obtaining the aqueous solution of(meth)acrylic acid.

More specifically, the synthesis reaction of (meth)acrylic acid may beconducted by the oxidation reaction of at least one compound selectedfrom the group consisting of propane, propylene, butane, isobutylene,and (meth)acrolein in the presence of a gas phase catalyst. Herein, thegas phase oxidation reaction may be progressed using a gas phaseoxidation reactor of a common structure and under common reactionconditions. As the catalyst for the gas phase oxidation reaction, commoncatalysts may be used, and for example, catalysts suggested in KoreanRegistered Patent No. 0349602 and No. 037818 and the like may be used.In the (meth)acrylic acid-containing mixed gas produced by the gas phaseoxidation reaction, in addition to the desired product, (meth)acrylicacid, non-reacted raw material compounds, intermediate (meth)acrolein,an inert gas, carbon dioxide, vapor, and various organic by-products(acetic acid, light ends, heavies, and the like) may be included.

Referring to FIGS. 1 and 2, the (meth)acrylic acid aqueous solution maybe obtained in the form of an aqueous solution in which (meth)acrylicacid is dissolved, by feeding a (meth)acrylic acid-containing mixed gas(1) to a (meth)acrylic acid absorption tower (100), to contact it withan absorption solvent, water.

Herein, the kind of the (meth)acrylic acid absorption tower (100) may bedetermined considering contact efficiency of the mixed gas (1) with theabsorption solvent, and the like. As non-limiting examples, the(meth)acrylic acid absorption tower (100) may be a packed column type ora multistage tray type. Inside the packed column type absorption tower,a filler such as a Raschig ring, a pall ring, a saddle, gauze,structured packing, and the like may be applied.

Considering the efficiency of the absorption process, the mixed gas (1)may be fed to the lower part of the absorption tower (100), and thesolvent including water may be fed to the upper part of the absorptiontower (100).

The absorption solvent may include water such as tap water, deionizedwater, and the like, and it may include recycled process waterintroduced from other processes (for example, an aqueous phase recycledfrom an extraction process and/or a distillation process). In theabsorption solvent, a trace amount of organic by-products introducedfrom other processes (for example, acetic acid) may be included.However, considering the absorption efficiency of (meth)acrylic acid, itis preferable that organic by-products may be included in a content of15 wt % or less in the absorption solvent fed to the absorption tower(100) (particularly, in the recycled process water).

Meanwhile, the (meth)acrylic acid absorption tower (100) may be operatedat an internal pressure of 1 to 1.5 bar or 1 to 1.3 bar, and an internaltemperature of 50 to 100° C. or 50 to 80° C., considering the watercontent according to saturated water vapor pressure and the condensationconditions of (meth)acrylic acid, and the like.

Through the absorption process, a low concentration (meth)acrylic acidaqueous solution having about 50 wt % or less of (meth)acrylic acid isdischarged to any one point corresponding to 30 to 70% from the highestpart of the (meth)acrylic acid absorption tower (100), and a highconcentration (meth)acrylic acid aqueous solution having about 50% ormore of (meth)acrylic acid is discharged to the lowest stage. Further,(meth)acrylic acid stripped non-condensable gas is discharged to theupper stage of the absorption tower.

The obtained (meth)acrylic acid aqueous solutions of a low concentrationand a high concentration may be fed to a water separation tower (300)through a transfer line (102) of a high concentration (meth)acrylic acidaqueous solution, or may be fed to a (meth)acrylic acid extraction tower(200) through a transfer line (103) of a low concentration (meth)acrylicacid aqueous solution, as shown in FIGS. 1 and 2.

Meanwhile, at least a part of the non-condensable gas discharged to theupper part of the (meth)acrylic acid absorption tower (100) may be fedto a process for recovering organic by-products (particularly, aceticacid) included in the non-condensable gas, and the remainder may be fedto a waste gas incinerator and discarded. That is, according to oneembodiment of the invention, a process of contacting the non-condensablegas with an absorption solvent to recover acetic acid included in thenon-condensable gas may be progressed.

The process of contacting the non-condensable gas with an absorptionsolvent may be conducted in an acetic acid absorption tower (150).Herein, for effective absorption of acetic acid, the acetic acidabsorption tower (150) may be operated at an internal pressure of 1 to1.5 bar, or 1 to 1.3 bar, and at an internal temperature of 50 to 100°C., or 50 to 80° C. In addition, specific operation conditions of theacetic acid absorption tower (150) may follow the disclosure of KoreanLaid-Open Patent Publication No. 2009-0041355.

Here, an absorption solvent (process water) for absorbing acetic acidmay be fed to the upper part of the acetic acid absorption tower (150),and an acetic acid-containing aqueous solution may be discharged to thelower part of the acetic acid absorption tower (150). Further, theacetic acid-containing aqueous solution may be fed to the upper part ofthe (meth)acrylic acid absorption tower (100) and used as an absorptionsolvent. The acetic acid-stripped non-condensable gas may be cycled tothe synthesis reaction process of (meth)acrylic acid and reused.

Extraction Process

The continuous recovery method of (meth)acrylic acid according to oneembodiment includes the step of contacting the low concentration(meth)acrylic acid aqueous solution with an extraction solvent includinga hydrophobic organic solvent in a (meth)acrylic acid extraction towerto extract (meth)acrylic acid.

The low concentration (meth)acrylic acid aqueous solution fed to theextraction tower (200) contacts an extraction solvent, and is dischargedas an extract in which a significant amount of (meth)acrylic acid isdissolved and a raffinate that is deprived of a significant amount of(meth)acrylic acid, respectively. Here, the low concentration(meth)acrylic acid aqueous solution is discharged at any one pointcorresponding to 30 to 70% from the highest part of the (meth)acrylicacid absorption tower, and it may include 1 to 50 wt % of (meth)acrylicacid, 50 to 95 wt % of water, and the remaining amount of organicby-products.

In the extraction tower (200), the extract that is a relatively lightphase is obtained through the upper outlet, and the raffinate that is arelatively heavy phase is obtained through the lower outlet of theextraction tower. Before the raffinate is discharged from the extractiontower (200), a certain amount thereof remains stationary at a stationarysection of the lower part of the extraction tower, and a part thereof isdischarged to the lower outlet of the extraction tower.

As such, by contacting the low concentration (meth)acrylic acid aqueoussolution with an extraction solvent in the extraction tower (200), mostwater included in the low concentration (meth)acrylic acid aqueoussolution may be removed. Thereby, a treatment load of the subsequentdistillation process may be lowered, thus improving energy efficiency ofthe total process. Furthermore, by lowering the treatment load of thedistillation process, polymerization of (meth)acrylic acid that may begenerated during distillation may be minimized, to secure more improvedrecovery efficiency of (meth)acrylic acid.

The extraction solvent fed to the extraction tower (200) includes ahydrophobic organic solvent, and organic by-products may be includedtherein. Specifically, the extraction solvent may include one or morehydrophobic organic solvents selected from the group consisting ofbenzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene,1-heptene, ethyl-benzene, methyl-cyclohexane, n-butyl acetate, isobutylacetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methylisobutyl ketone, 2-methyl-1-heptene, 6-methyl-1-heptene,4-methyl-1-heptene, 2-ethyl-1-hexene, ethylcyclopentane,2-methyl-1-hexene, 2,3-dimethylpentane, 5-methyl-1-hexene, andisopropyl-butyl-ether.

The weight ratio of the extraction solvent to water in the lowconcentration (meth)acrylic acid aqueous solution fed to the step ofextracting (meth)acrylic acid may be 2.7 or more, preferably 3.0 ormore, and more preferably 3.0 to 5.0. As such, by controlling the amountof the extraction solvent used in the extraction process, the reflux ofthe solvent may be increased in the subsequent distillation process,thereby further increasing the recovery rate of (meth)acrylic acid.

In the extraction process, if the weight ratio of the extraction solventto water in the low concentration (meth)acrylic acid aqueous solution isless than 2.7, (meth)acrylic acid extraction efficiency may be lowered,which is not preferable. Further, if the weight ratio of the extractionsolvent to water in the low concentration (meth)acrylic acid aqueoussolution is greater than 5.0, although the extraction efficiency may beimproved as the weight ratio of the extraction solvent to water in the(meth)acrylic acid aqueous solution increases, the amount of theextraction solvent to be distilled in the subsequent solvent recoveryprocess may excessively increase, which is not preferable.

As the extraction tower (200), common extraction towers of aliquid-liquid contact type may be used without specific limitations. Asnon-limiting examples, the extraction tower (200) may be a Karr type ofreciprocating plate column, a rotary-disk contactor, a Scheibel column,a Kuhni column, a spray extraction tower, a packed extraction tower, apulsed packed column, and the like.

Through the extraction process, a (meth)acrylic acid extract isdischarged to the upper part of the extraction tower (200), and thedischarged extract is fed to a solvent recovery tower (250) through atransfer line (203). In addition, a raffinate is discharged to the lowerpart of the extraction tower (200), and the discharged raffinate is fedto a phase separation tank (350) through a transfer line (201), treated,and recycled.

Herein, in the extract, in addition to a desired compound, (meth)acrylicacid, an extraction solvent, water, and organic by-products may beincluded. According to one embodiment, under a steady state where stableoperation is conducted, 5 to 13 wt % of (meth)acrylic acid, 85 to 93 wt% of an extraction solvent, 0.01 to 2 wt % of water, and the remainingamount of organic by-products may be included in the extract. That is,most water included in the (meth)acrylic acid aqueous solution may berecovered as a raffinate through the extraction process. As most wateris recovered from the extraction tower (200), a distillation load of adistillation process may be reduced to lower energy consumption.Further, since distillation conditions may be relaxed, polymerization of(meth)acrylic acid may be minimized in the distillation process, thussecuring operation stability and improving recovery efficiency of(meth)acrylic acid.

The raffinate discharged from the extraction tower (200) may consistmostly of water, and a part of non-extracted (meth)acrylic acid andby-products may be included therein. However, according to oneembodiment of the invention, a very small amount, such as 15 wt % orless, or 0.1 to 5 wt %, of (meth)acrylic acid may be included in theraffinate, thus minimizing the loss of (meth)acrylic acid in theabsorption process and extraction process.

Solvent Recovery Process

The continuous recovery method of (meth)acrylic acid according to oneembodiment includes the step of heating the (meth)acrylic acid extractobtained in the extraction process in a solvent recovery tower torecover the solvent.

The extract discharged through the upper outlet of the (meth)acrylicacid extraction tower (200) is fed to the solvent recovery tower (250)through the transfer line (203). By supplying heat through a reboiler atthe lower stage of the recovery tower, the extraction solvent isrecovered through the upper outlet, and the (meth)acrylic acid extractexcluding the recovered extraction solvent is obtained through the loweroutlet.

The temperature of the lower part of the solvent recovery tower (250) ofone embodiment may be 100° C. or less. The “lower part” of the solventrecovery tower means at least any one point within 10% from the loweststage of the solvent recovery tower.

The pressure of the highest stage of the solvent recovery tower (250)may be atmospheric pressure to 20 torr, for efficient distillation ofthe extract.

Meanwhile, the solvent recovered in the solvent recovery step mayinclude 99 wt % or more of a hydrophobic organic solvent. Morespecifically, the recovered solvent may include 1 wt % or less,preferably 0.5 wt % or less, and more preferably 0.3 wt % or less of(meth)acrylic acid, in addition to the hydrophobic organic solvent.

The feed excluding the solvent recovered in the (meth)acrylic acidextract may include 5 to 70 wt % of (meth)acrylic acid, 30 to 95 wt % ofa hydrophobic organic solvent, and the remaining amount of organicby-products.

A part of the solvent recovered in the solvent recovery step may berefluxed to the solvent recovery tower, and the remaining part may befed to the upper stage of the water separation tower or to the phaseseparation tank and recycled.

As such, according to the continuous recovery method of (meth)acrylicacid of one embodiment, the extraction solvent is recovered through thesolvent recovery process, and the amount of an azeotropic solventintroduced as a reflux of the water separation tower may be increased byas much as the amount of the extraction solvent recovered in the solventrecovery process, and thus the liquid/gas flow behavior in the uppertray of the feed introduction stage of the water separation tower may bestabilized and the recovery efficiency of (meth)acrylic acid may beimproved.

Distillation Process

The continuous recovery method of (meth)acrylic acid according to oneembodiment includes the step of distilling the feed excluding thesolvent recovered in the (meth)acrylic acid extract and the highconcentration (meth)acrylic acid aqueous solution in a water separationtower to obtain (meth)acrylic acid.

According to one embodiment of the invention, the feed is the remainderof the (meth)acrylic acid extract fed from the above-explainedextraction process excluding the solvent recovered in the solventrecovery process, and the feed is fed to the water separation tower(300) from the solvent recovery tower (250) through the transfer line(253), as shown in FIGS. 1 and 2.

The high concentration (meth)acrylic acid aqueous solution is thesolution discharged to the lowest stage of the absorption tower, whichis obtained by contacting the mixed gas produced by the synthesisreaction of (meth)acrylic acid, including (meth)acrylic acid, organicby-products, and water vapor, with water in the (meth)acrylic acidabsorption tower, and it is fed to the water separation tower (300) fromthe (meth)acrylic acid absorption tower (100) through the transfer line(102), as shown in FIGS. 1 and 2.

Here, in order to achieve efficient distillation, it is preferable thatthe feed and the high concentration (meth)acrylic acid aqueous solutionare fed to any one stage corresponding to 25 to 75% or any one stagecorresponding to 25 to 50% from the highest stage, based on the totalnumber of stages of the water separation tower.

If the feed and the high concentration (meth)acrylic acid aqueoussolution are fed to the point exceeding 75% from the highest stage ofthe water separation tower (300), a part of the water to be recovered asthe upper discharge liquid of the water separation tower that isincluded in the feed and the aqueous solution, and the extractionsolvent, are included in the lower discharge liquid of the waterseparation tower, which is not preferable. If they are fed to the pointless than 25% from the highest stage of the water separation tower, theconcentration of acrylic acid included in the upper discharge liquid ofthe water separation tower may increase, and thus the acrylic acidrecovery rate of the water separation tower may be lowered.

The feed fed to the water separation tower (300) is made to come incontact with an azeotropic solvent introduced into the upper part, andheated to an optimum temperature, thereby achieving distillation byevaporation and condensation.

Herein, in order to effectively separate (meth)acrylic acid included inthe feed from the remaining components (for example, water, acetic acid,extraction solvents, and the like), the distillation is preferablyconducted by azeotropic distillation.

A solvent used for the azeotropic distillation is preferably ahydrophobic azeotropic solvent that may form an azeotrope with water andacetic acid, and may not form an azeotrope with (meth)acrylic acid. Thehydrophobic azeotropic solvent preferably has a lower boiling point thanthat of (meth)acrylic acid (for example, a boiling point of 120° C. orless, 10 to 120° C., or 50 to 120° C.).

Specifically, the hydrophobic azeotropic solvent may be at least oneselected from the group consisting of benzene, toluene, xylene,n-heptane, cycloheptane, cycloheptene, 1-heptene, ethyl-benzene,methyl-cyclohexane, n-butyl acetate, isobutyl acetate, isobutylacrylate, n-propyl acetate, isopropyl acetate, methyl isobutyl ketone,2-methyl-1-heptene, 6-methyl-1-heptene, 4-methyl-1-heptene,2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-1-hexene,2,3-dimethylpentane, 5-methyl-1-hexene, and isopropyl-butyl-ether.

Considering production efficiency according to a continuous process, itis preferable that the hydrophobic azeotropic solvent is identical tothe extraction solvent of the extraction process. As such, if the samekinds of solvents are used in the extraction process and thedistillation process, at least a part of the solvent that is distilledin the water separation tower (300) and recovered through a phaseseparation tank (350) may be fed to the (meth)acrylic acid extractiontower (200) and reused as an extraction solvent.

Through the distillation process, among the feed, components other than(meth)acrylic acid are discharged to the upper part of the distillationtower (300) together with the azeotropic solvent, and (meth)acrylic acidis discharged to the lower part of the distillation tower (300).

The upper discharge liquid of the water separation tower (300) may befed to the phase separation tank (350) and reused after a predeterminedtreatment. Herein, the phase separation tank (350) is an apparatus forseparating immiscible liquids by gravity or centrifugal force and thelike, wherein a relatively light liquid (for example, an organic phase)may be recovered from the upper part of the phase separation tank (350)and a relatively heavy liquid (for example, an aqueous phase) may berecovered from the lower part of the phase separation tank (350).

For example, the upper discharge liquid of the water separation tower(300), and a part of the raffinate discharged in the above-explainedextraction tower (200) and the solvent recovered in the solvent recoverytower (250) may be separated into an organic phase including a solventand an aqueous phase including water, in the phase separation tank(350). The separated organic phase may be fed to the upper part of thewater separation tower (300) and used as an azeotropic solvent.

If necessary, at least a part of the organic phase may be fed to theextraction tower (200) and used as an extraction solvent. Further, atleast a part of the aqueous phase separated in the phase separation tank(350) may be fed to the (meth)acrylic acid absorption tower (100) andused as an absorption solvent, and a part thereof may be treated aswaste water. In the aqueous phase, acetic acid may be partly included,and the concentration of acetic acid included in the aqueous phase mayvary according to the kind of azeotropic solvents, the reflux ratio, andthe like.

Meanwhile, while the (meth)acrylic acid aqueous solution passes throughthe (meth)acrylic acid absorption tower (100), the extraction tower(200), the solvent recovery tower (250), the water separation tower(300), and the like, at least a part of (meth)acrylic acid included inthe aqueous solution may form dimers or oligomers. To minimize suchpolymerization of (meth)acrylic acid, common polymerization inhibitorsmay be added to the water separation tower (300).

In the lower discharge liquid of the water separation tower (300), inaddition to (meth)acrylic acid, heavies such as a polymer of(meth)acrylic acid, polymerization inhibitors, and the like may beincluded. Thus, if necessary, a step of feeding the lower dischargeliquid of the water separation tower (300) to a heavies separation tower(400) and separating heavies included in the lower discharge liquid maybe further conducted. Crude (meth)acrylic acid (CAA) recovered throughthe process may be passed through an additional crystallization processand obtained as high purity (meth)acrylic acid (HPAA). Herein, theheavies separation process, the crystallization process, and the likemay be conducted under common conditions, and the process conditions arenot specifically limited.

In the method of continuous recovery of (meth)acrylic acid, each of theabove-explained steps may be conducted organically and continuously. Inaddition to the above-explained steps, processes that can be commonlyconducted before, after, or simultaneously with each step may be furtherincluded.

II. An Apparatus for Continuous Recovery of (Meth)Acrylic Acid

According to another embodiment of the invention, an apparatus forcontinuous recovery of (meth)acrylic acid is provided, including:

a (meth)acrylic acid absorption tower (100) equipped with a mixed gasinlet to which a mixed gas including (meth)acrylic acid, organicby-products, and water vapor, produced by the synthesis reaction of(meth)acrylic acid, is fed, in which a low concentration (meth)acrylicacid aqueous solution outlet, at which a low concentration (meth)acrylicacid aqueous solution obtained by the contact of the mixed gas withwater is discharged, is installed at any one point corresponding to 30to 70% from the highest part, and a high concentration (meth)acrylicacid aqueous solution outlet is installed at the lowest stage;

a (meth)acrylic acid extraction tower (200) equipped with an aqueoussolution inlet that is connected with the low concentration(meth)acrylic acid aqueous solution outlet of the absorption tower (100)through an aqueous solution transfer line (103), an extract outlet atwhich a (meth)acrylic acid extract obtained by the contact of theintroduced (meth)acrylic acid aqueous solution with an extractionsolvent is discharged, and a raffinate outlet at which a raffinate isdischarged;

a solvent separation tower (250) equipped with an extract inlet that isconnected with the extract outlet of the extraction tower (200) throughan extract transfer line (203), an upper stage outlet at which thesolvent obtained by heating the introduced extract is discharged, and alower stage outlet at which the feed excluding the solvent recoveredfrom the extract is discharged; and

a water separation tower (300) equipped with a feed inlet that isconnected with the lower stage outlet of the solvent separation tower(250) through a transfer line (253), and is connected with the(meth)acrylic acid aqueous solution outlet of the (meth)acrylic acidabsorption tower (100) through a transfer line (102), and a(meth)acrylic acid outlet at which (meth)acrylic acid obtained by thedistillation of the introduced feed is discharged,

wherein the apparatus is operated such that the weight ratio of theextraction solvent to water in the low concentration (meth)acrylic acidaqueous solution fed to the (meth)acrylic acid extraction tower (200) is2.7 or more.

That is, in the apparatus of one embodiment, basically, the(meth)acrylic acid absorption tower (100) is connected with the(meth)acrylic acid extraction tower (200) through the transfer line(103) of the low concentration (meth)acrylic acid aqueous solution. Inaddition, the (meth)acrylic acid extraction tower (200) is connected tothe solvent recovery tower (250) through the (meth)acrylic acid extracttransfer line (203), and the solvent recovery tower (250) is connectedwith the water separation tower (300) through the transfer line (253) ofthe feed excluding the solvent recovered in the extract.

Particularly, in the apparatus for continuous recovery of (meth)acrylicacid of one embodiment, the outlet of the low concentration(meth)acrylic acid aqueous solution is positioned at any one pointcorresponding to 30 to 70% from the highest part of the (meth)acrylicacid absorption tower (100), and the outlet of the high concentration(meth)acrylic acid aqueous solution is positioned at the lowest stage.

A feed inlet that is connected with the lower outlet of the solventrecovery tower (250) through the transfer line (253), and is connectedwith the (meth)acrylic acid aqueous solution outlet of the (meth)acrylicacid absorption tower (100) through the transfer line (102), may bepositioned at any one stage corresponding to 25 to 75% or 25 to 50% fromthe highest stage, based on the total number of stages of the waterseparation tower (300).

The (meth)acrylic absorption tower (100) may be a packed column type, ora multistage tray type, and inside of the packed column type of tower,fillers such as a Raschig ring, a pall ring, a saddle, gauze, structuredpacking, and the like may be applied.

As the (meth)acrylic acid extraction tower (200), common extractiontowers of a liquid-liquid contact type may be used without specificlimitation. As non-limiting examples, the extraction tower may be a Karrtype of reciprocating plate column, a rotary-disk contactor, a Scheibelcolumn, a Kuhni column, a spray extraction tower, a packed extractiontower, a pulsed packed column, and the like.

The solvent recovery tower (250) and the water separation tower (300)may be a packed column including the above-described fillers inside or amultistage column, preferably equipped with a sieve tray column, or adual flow tray column, and the like.

In addition, the acetic acid absorption tower (150), the (meth)acrylicacid aqueous solution transfer line (103), the extract transfer line(203), the phase separation tank (350), the heavies separation tower(400), and the like, as shown in FIGS. 1 and 2, may have constructionscommon in the technical field to which the invention pertains.

Advantageous Effects

The continuous recovery method of (meth)acrylic acid according to thepresent invention can secure a high (meth)acrylic acid recovery ratethrough the solvent recovery process, and simultaneously enables stable(meth)acrylic acid recovery and the operation of a continuous process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the method and apparatus for continuousrecovery of (meth)acrylic acid according to one embodiment of thepresent invention.

FIG. 2 schematically shows the method and apparatus for continuousrecovery of (meth)acrylic acid according to another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, preferable examples are presented to aid in understandingof the invention. However, these examples are only to illustrate theinvention, and the scope of the invention is not limited thereto.

EXAMPLES

Using the apparatus with the construction of FIG. 1, the process forcontinuously recovering acrylic acid was conducted as follows.

(Extraction Process)

Among the acrylic acid aqueous solution of a low concentration (103)discharged to the side part of the absorption tower (100) (composition:acrylic acid 21.06 wt %, acetic acid 4.15 wt %, and water 74.79 wt %),acrylic acid was extracted using toluene introduced through anextraction solvent transfer line (302) according to a liquid-liquidcontact method. The extract (203) was discharged to the upper part ofthe extraction tower (200), and the raffinate was discharged to thelower part of the extraction tower and it may be recycled to the highestpart of the acrylic acid absorption tower (100) through the raffinatetransfer line (201).

As the acrylic acid extraction tower (200), a Karr type of reciprocatingplate column having a total of 56 stages with an inner diameter of 22 mmwas used. The acrylic acid aqueous solution of a low concentration (103)discharged to the side part of the absorption tower (100) was introducedthrough the highest stage, i.e., the first stage of the extraction tower(200), at a flow rate of 23.8 g/min. Further, a part of the reflux flowincluding toluene obtained as an organic layer in the upper dischargeliquid of the water separation tower (300) was used as the extractionsolvent (composition: acrylic acid at about 0.27 wt %, acetic acid atabout 0.48 wt %, the balance being toluene) of the extraction tower(200), wherein the extraction solvent was introduced through the loweststage, i.e., the 56th stage of the extraction tower (200), at a flowrate of 59.44 g/min.

After stable operation was conducted, under a steady state, an acrylicacid extract (composition: toluene at about 91.32 wt %, acrylic acid atabout 7.42 wt %, water at about 0.62 wt %, and acetic acid at about 0.64wt %) was obtained at the upper part of the extraction tower (200) at aflow rate of 64.59 g/min, and the remaining raffinate (composition:water at about 93.36 wt %, acrylic acid at about 2.03 wt %, and aceticacid at about 4.61 wt %) was discharged to the lower part of theextraction tower (200).

As a result of operating the acrylic acid extraction tower (200), thewater removal rate for the low concentration acrylic acid aqueoussolution discharged from the side part of the acrylic acid absorptiontower was 97.8%, and the acrylic acid extraction rate was 92.7%. Here,the ratio of the extraction solvent introduced into the extractiontower/water was 3.3.

(Solvent Recovery Process)

As the solvent recovery tower (250), a dual flow tray column having atotal of 15 stages with an inner diameter of 20 mm was used, and theoperation pressure was maintained at 100 torr. The upper extract (203)of the extraction tower (200) of the extraction process was introducedinto the lowest stage of the solvent recovery tower (250) at 0.98 g/min.Further, among the upper flow of the solvent recovery tower (250), areflux flow (252) was introduced into the highest stage, i.e. the firststage of the solvent recovery tower (250), at a flow rate of 4.41 g/min.

Heat was supplied through the reboiler of the lower stage of the solventrecovery tower (250) such that a flow (251) excluding the reflux amongthe upper flow of the solvent recovery tower became 50 mass %, based onthe extract introduced into the solvent recovery tower. After stableoperation was conducted for about 4 hours, under a steady state, theflow (251) excluding the reflux among the upper flow of the solventrecovery tower was discharged at a flow rate of 0.49 g/min, and thelower flow (253) of the solvent recovery tower was discharged at a flowrate of 0.49 g/min. Here, the upper temperature and the lowertemperature of the solvent recovery tower (250) were maintained at 49°C. and 62° C., respectively. Among the upper flow of the solventrecovery tower, the flow (251) excluding the reflux and the reflux flow(252) exhibited the compositions of 0.32 wt % of acrylic acid, 0.51 wt %of acetic acid, and 99.17 wt % of toluene, and the lower flow of thesolvent recovery tower (250) exhibited the composition of 19.765 wt % ofacrylic acid, 0.49 wt % of acetic acid, and 79.75 wt % of toluene. Theacrylic acid recovery rate of the solvent recovery tower (250) was98.4%, and the toluene stripping ratio was 55.6%.

(Distillation Process)

As the water separation tower (300), a sieve tray (including a downcorner) column having a total of 39 stages with an inner diameter of 70mm was used, and the operation pressure was maintained at 110 torr. Thelower flow (253) of the solvent recovery tower (250) of the solventrecovery process was introduced into the 17th stage from the upper partof the water separation tower (300) at a flow rate of 17.3 g/min, and alower discharge liquid (102) of the acrylic acid absorption tower (100)was introduced into the 19th stage from the upper part of the waterseparation tower (300) at a flow rate of 55.1 g/min. Further, the flow(251) excluding the reflux flow among the upper flow of the solventrecovery tower (250) was introduced into the phase separation tank (350)at a flow rate of 22.6 g/min, and a part of the toluene reflux flowseparated from the phase separation tank (350) was introduced into thehighest stage, i.e., the first stage of the water separation tower(300), at a flow rate of 54.3 g/min. Here, the mass ratio of the toluenein the reflux introduced into the upper part of the water separationtower and the toluene in the flow (251) excluding the reflux among theupper flow of the solvent recovery tower introduced into the feedintroduction stage of the water separation tower was 3.7:1.

Heat was supplied through the reboiler of the lower stage of the waterseparation tower (300) to control such that the temperature of the feedintroduction stage became 68.6° C., and the temperature of the 21thstage at the lower part of the feed introduction stage became 80° C. ormore. After stable operation was conducted for about 6 hours, under asteady state, the distillate consisting of an organic phase and anaqueous phase was discharged at 37.20 g/min and 11.80 g/min,respectively, and acrylic acid flow to the lower part of the waterseparation tower (300) was 46.00 g/min. Here, under a steady state, theupper temperature of the water separation tower (300) was maintained at40.9° C. and the lower temperature was maintained at 94.3° C. An organicphase distillate (304) exhibited a composition of 0.23 wt % of acrylicacid, 0.48 wt % of acetic acid, and 99.29 wt % of toluene, and the lowerflow (303) of the water separation tower had a composition of 98.58 wt %of acrylic acid, 2100 ppm of acetic acid, and 1.42 wt % of heavies andpolymerization inhibitor. The acrylic acid recovery rate of the waterseparation tower (300) was 99.8%.

Comparative Example

A process for continuous recovery of acrylic acid was conducted by thesame method as in the example, except that a distillation processdescribed below was progressed immediately after the extraction process,without the solvent recovery process.

(Distillation Process)

As the water separation tower (300), a sieve tray (including a downcorner) column having a total of 39 stages with an inner diameter of 70mm was used, and the operation pressure was maintained at 110 torr. Thelower discharge liquid (102) of the acrylic acid absorption tower (100)and the upper extract (203) of the extraction tower (200) of Example 1were introduced into the 20th stage from the upper part of the waterseparation tower (300) at 44.99 g/min and 36.4 g/min, respectively.Further, a part of the toluene reflux flow separated from the phaseseparation tank (350) was introduced into the highest stage, i.e., thefirst stage of the water separation tower (300), at a flow rate 22.22g/min. Here, the mass ratio of the toluene in the reflux introduced intothe upper part of the water separation tower and the toluene in theupper extract (203) of the extraction tower introduced into the feedintroduction stage of the water separation tower was 0.66:1.

Heat was supplied through the reboiler of the lower stage of the waterseparation tower (300) to control such that the temperature of the feedintroduction stage became 64.6° C., and the temperature of the 15thstage did not exceed about 46° C. After stable operation was conductedfor about 6 hours, under a steady state, the distillate consisting of anorganic phase and an aqueous phase was discharged to the upper part ofthe water separation tower (300) at 33.86 g/min and 8.50 g/min,respectively, and acrylic acid flow to the lower part of the waterseparation tower (300) was 39.03 g/min. Here, under a steady state, theupper temperature of the water separation tower (300) was maintained at42.4° C., and the lower temperature was maintained at 92.3° C. Theorganic phase distillate (304) exhibited a composition of 0.73 wt % ofacrylic acid, 0.76 wt % of acetic acid, and 98.51 wt % of toluene, andthe lower flow (303) of the water separation tower exhibited acomposition of 98.15 wt % of acrylic acid, 3000 ppm of acetic acid, and1.85 wt % of acrylic acid polymer and polymerization inhibitor. Theacrylic acid recovery rate of the water separation tower (300) was98.7%.

REFERENCE NUMERALS

-   -   1: (meth)acrylic acid-containing mixed gas    -   100: (meth)acrylic acid absorption tower    -   102: high concentration (meth)acrylic acid aqueous solution        transfer line    -   103: low concentration (meth)acrylic acid aqueous solution        transfer line    -   150: acetic acid absorption tower    -   200: (meth)acrylic acid extraction tower    -   201: raffinate transfer line    -   203: extract transfer line    -   250: solvent recovery tower    -   251: flow excluding the reflux among the upper flow of the        solvent recovery tower    -   252: reflux flow among the upper flow of the solvent recovery        tower    -   253: lower flow of the solvent recovery tower    -   300: water separation tower    -   301: azeotropic solvent transfer line    -   302: extraction solvent transfer line    -   303: lower flow of the water separation tower    -   304: upper flow of the water separation tower    -   305: absorption solvent (water) transfer line    -   350: phase separation tank    -   400: heavies separation tower

The invention claimed is:
 1. An apparatus for continuous recovery of(meth)acrylic acid, comprising a (meth)acrylic acid absorption towerequipped with a mixed gas inlet to which a mixed gas feed comprising(meth)acrylic acid, organic by-products, and water vapor, produced by asynthesis reaction of (meth)acrylic acid, is fed, in which a lowconcentration (meth)acrylic acid aqueous solution outlet, at which a lowconcentration (meth)acrylic acid aqueous solution obtained by contact ofthe mixed gas with water is discharged, is installed at a position thatis 30% to 70% lower than a highest point of the (meth)acrylic acidabsorption tower, and a high concentration (meth)acrylic acid aqueoussolution outlet, at which a high concentration (meth)acrylic acidaqueous solution is discharged, is installed at a lowest of a pluralityof stages, wherein the low concentration (meth)acrylic acid aqueoussolution comprises 50 wt % or less of (meth)acrylic acid and the highconcentration (meth)acrylic acid aqueous solution comprises 50 wt % ormore of (meth)acrylic acid; a (meth)acrylic acid extraction towerequipped with an aqueous solution inlet that is connected with the lowconcentration (meth)acrylic acid aqueous solution outlet of the(meth)acrylic acid absorption tower through an aqueous solution transferline, an extract outlet at which a (meth)acrylic acid extract obtainedby contact of the (meth)acrylic acid aqueous solution, which is inputfrom the (meth)acrylic acid absorption tower through the aqueoussolution transfer line, with an extraction solvent is discharged, and araffinate outlet at which a raffinate is discharged; a solventseparation tower equipped with an extract inlet that is connected withthe extract outlet of the (meth)acrylic acid extraction tower through anextract transfer line, an upper stage outlet at which a solvent obtainedby heating the (meth)acrylic acid extract, which is introduced throughthe extract inlet, is discharged, and a lower stage outlet at which afeed excluding the solvent recovered from the (meth)acrylic acid extractis discharged; and a water separation tower equipped with a feed inlet,through which the feed excluding the solvent recovered from the(meth)acrylic acid extract is fed, and that is connected with the lowerstage outlet of the solvent separation tower through a transfer line,and is connected with the high concentration (meth)acrylic acid aqueoussolution outlet of the (meth)acrylic acid absorption tower through atransfer line, and a (meth)acrylic acid outlet at which (meth)acrylicacid obtained by distillation of the feed excluding the solventrecovered from the (meth)acrylic acid extract is discharged, wherein theapparatus is operated such that a weight ratio of the extraction solventto water in the low concentration (meth)acrylic acid aqueous solutionfed to the (meth)acrylic acid extraction tower is 2.7 or more.
 2. Theapparatus according to claim 1, wherein the feed inlet that is connectedwith the lower stage outlet, at which the feed excluding the solventrecovered from the (meth)acrylic acid extract is discharged, and isconnected with the high concentration (meth)acrylic acid aqueoussolution outlet of the (meth)acrylic acid absorption tower through atransfer line, is positioned at a stage that is 25% to 75% lower than afirst top stage of the water separation tower, based on a total numberof stages of the water separation tower.